1. Field of the Invention
The present invention relates generally to the breeding of tomato plants. More specifically, the invention relates to the introduction of a genetic factor that confers on tomato plants the ability to bear mature fruit which accumulate sucrose, thereby increasing the total soluble solids content of the fruit.
2. Information Disclosure
In the prior art, increasing the soluble solids content of tomato fruit has been attempted by introducing the high soluble solids trait from wild Lycopersicon species. Rick, Hilgardia, 42:494-509 (1974), used L. chmielewskii in a breeding plan to produce a variety, known as LA 1563, which showed an increase in soluble solids content. Genetic analysis of this variety indicated that the high soluble solids trait was dominant and was controlled by a number of loci. Restriction fragment length polymorphisms have also been used to create linkage maps of the loci that are associated with the trait. Paterson et al., Nature, 335:721-726 (1988).
Investigations of carbohydrate metabolism in tomato reveal that fruit of tomato cultivars accumulate glucose and fructose, but not sucrose. Yelle et al., Plant Physiol, 87:737-740 (1988). The rate of carbohydrate import, a determinant of soluble solids content of the tomato fruit, has been reported to be inversely proportional to sucrose concentration in the fruit. Walker and Thornley, Ann. Bot., 41:977-985 (1977).
The fruit of three other Lycopersicon species (L. chmielewskii, L. hirsutum, and L. peruvianum) have been shown to have a high soluble solids content. Accessions of these species accumulate sucrose instead of glucose and fructose. Davies, Nature, 209:640-641 (1966). The prior art, however, provided no teaching as to whether this trait was under the control of one or many loci. Studies also show that these species have very low acid invertase level compared to L. esculentum. Manning and Maw, Phytochemistry, 14:1965-1969 (1975) and Yelle at al., supra. The fruit of the high solids variety produced by Rick, LA 1563, has been shown not to accumulate sucrose. Hewitt et al., J. Amer. Soc. Hort. Soc., 107, 896-900 (1982). This result suggests that the L. chmielewskii trait for sucrose accumulation was not genetically fixed in LA 1563.